Desktop Software Upgrade Fatal Error

I am trying to upgrade my BB desktop software to 4.5 as I was instructed to by a message from RIM. But every time I try, I get a message that says A fatal error has occurred while updating your device's software. Please try again. It hangs up at the same place in the process--after it has backed up everything on the device. It says something like "uploading 450 of 540" and it stops. Any ideas out there?